What
about life in deep space, for instance on comets and asteroids,
or even on meteorites? Comets,
asteroids and meteorites are essentially unaltered materials from
the formation of the Solar System. Some
meteorites, and probably all comets,
contain organic chemical compounds.

One
of the most fundamental questions about the origins of life on
Earth was revived in the public's mind in the late 1970's, by
the astronomers Professor Sir Fred Hoyle of Cambridge University,
in England, and Professor Chandra Wickramasinghe, of Cardiff University
in Wales. They published a highly controversial paper in
The New Scientist magazine. It revived Lord
Kelvin's ideas from more than a hundred years previously by
suggesting that perhaps life had not begun on Earth at all, but
had been seeded to Earth by comet and asteroid impact. The
theory is now known as Panspermia.

If
this idea was not sufficiently debatable, they went on enrage
many scientists by suggesting that influenza viruses originated
in the ice of comets and the meteor
streams left by comet tails. Their case was unconvincing
to many who read the article, but the Panspermia
idea had taken seed. Others thought about it, not least
the world's space agencies, and while almost no-one accepted the
notion of "Space
Flu", the overall concept did not seen as far-fetched
as it had done before the Russian and NASA missions to other planets
in the Solar System, which had started in the mid 1960's.

This
was not surprising for other people had been thinking along similar
lines, but had not attracted the public attention nor the wrath
of their fellow scientists. One of the earliest was Juan
Oró of Houston University, in 1961 and Sherwood
Chang at NASA Ames, in 1979. More recently Christopher
Chyba of the SETI Institute
has been a keen advocate of Panspermia.

Comets
(Visit: Comets
Home from University of Hawaii) are now accepted to be good
candidates as life-carriers in the form of micro-organisms such
as bacteria or viruses. They have many of the right ingredients
- organic compounds, carbon, water, and perhaps they can become
warm enough to allow carbon life processes to start to work.

When
a planetary system forms, hundreds of billions of comets (See
Kuiper
Belt Objects) condense from the hot dusty debris and gas that
is the raw material for their formation. Most of these occupy
the dark, cold outer regions. The comets
are composed of ice, rocky material such as silicates and a cocktail
of elementary chemicals - eg carbon, Sulfur, phosphorus
- and simple compounds - eg ammonia, methane.

At
the time of cometry formation the temperatures inside a forming
comet may be are high enough to permit chemical reactions to occur
at a rapid rate and even, perhaps for water to be liquid.
If this is the case, then the conditions and basic chemicals of
life could exist inside a comet. Recent experiments
and discoveries by teams of researchers such as the Laboratory
Astrophysics Group, at NASA Ames, suggest that life might
just be able to come into being in such conditions. And
if this is so, then it is likely that the life that forms is bacterial
or archaean in nature
.

Not
only do comets appear to contain the ingredients for life, they
also contain the nutrients to allow replication and multiplication,
so that a comet might even be largely made up living entities!
In fact, it has been discovered that the infrared
signatures of comets, including Hale-Bopp and Halley, are
identical to that of bacteria. But we should not accept
this as certain proof, for other
materials have the same signature.

Conditions
in a comet might at first sight appear too extreme for life.
Low temperatures and pressures and high levels of radiation should
mitigate against the survival of life. Many, if not most
microbes on Earth live in extreme conditions,
however. Survival in space should be no problem for suitably
adapted organisms.

The
truth about cometry habitats, however, will not be answered until
we have examined at least one comet at close hand. NASA,
ESA and NASDA
are all working on comet rendezvous projects, to retrieve samples
of material for analysis. Within the next decade,
some of the most important questions in the interstellar
life debate may have been answered.